To prepare the cake layers, pour all of the listed ingredients in a pot and stir until it comes to a boil on low heat - let it thicken and gain a slightly golden color.
Let the mixture cool and pour in the flour. Knead the dough gradually and divide it up into 5 equal-sized balls. Roll out each one into a thin and round layer. Place 1 layer in a tray with baking paper. Bake each at 356°F (180°C) for 5-6 min.
While still warm, shape each ready layer into a round form, so that all layers are the same and the cake turns out beautiful. Do this while layers are still hot because after they cool, they harden and cutting becomes difficult.
For the cream mixture, stir the sour cream and sugar well with a fork.
Start stacking the cake layers, smearing cream mixture in between them + blueberry jam. Finally, smear the whole cake with cream and sprinkle generously with ground walnuts.
Leave the French cake in the fridge to soften.